Study On The Structure And Properties Of Ion-doped Na_0.5Bi_2.5Nb₂O₉ Bismuth Layered Piezoelectric Ceramics

As one of the important members of piezoelectric materials,Na_0.5Bi_2.5Nb₂O₉（NBN）based bismuth layered piezoelectric ceramics have high Curie temperature（T_c～780℃）,low dielectric loss,and good high temperature stability,so that it has potential application prospects in high-temperature piezoelectric sensors,capacitors,storage,etc.Nevertheless,the poor piezoelectric activity of NBN based ceramics due to structural anisotropy and large coercivity field E_crestrict their practical application.Therefore,this paper adopts the method of ion doping modification,taking NBN as the matrix,substituting Co³⁺acceptor for Nb⁵⁺at B site,and then doping through the Co/W ion co-doping at the B site,and further through the co-doping of A site（LiCe）ions on this basis,and analyzing its influence on the crystal structure and electrical properties of NBN ceramics.Firstly,Co³⁺doped Na_0.5Bi_2.5Nb_2-xCo_xO₉（NBNC-x,0.00≤x≤0.09）bismuth layered piezoelectric ceramics were synthesized by the traditional solid-state method.The microstructure,piezoelectric,dielectric and ferroelectric properties of Co³⁺doped NBNC-x ceramics were systematically investigated.The XRD results showed all ceramics possess two-layer Aurivillius structure.With the increase of Co³⁺doping,the distortion of the ceramic samples increases,the grain size become larger,and the Curie temperature increase from 778 to 793℃.Moreover,the Co³⁺doping significantly enhance piezoactivity(d₃₃)and ferroelectricity（P_r）,and reduce dielectric loss（tanδ）.The Na_0.5Bi_2.5Nb_1.93Co_0.07O₉ceramic exhibited the best electrical properties:d₃₃=20.1 pC/N,T_c=793℃,P_r=4.22μC/cm~2.Secondly,Na_0.5Bi_2.5Nb_2-x(Co_1/3W_2/3)_xO₉（NBNCW-x,0.00≤x≤0.05）bismuth layered piezoelectric ceramics were prepared by Co/W ions co-doping the B-site Nb⁵⁺.The influence of Co/W co-doping on the structure and electrical properties of NBNCW-x ceramics was systematically studied.The XRD and Rietveld refinement results showed that the samples lattice distortion decreased with the increment of Co/W doping.The XPS results showed that the number of oxygen vacancies in the NBNCW-x ceramics could be reduced by the substitution of a small amount of Co/W.The weakened lattice distortion and reduced number of oxygen vacancies of the NBNCW-x ceramics synergistically contributed to its improved electrical properties.In particular,the Na_0.5Bi_2.5Nb_1.97(Co_1/3W_2/3)_0.03O₉ceramic exhibited the best electrical properties,and its T_c,d₃₃and P_rwere 780°C,24.9 pC/N and 12.6μC/cm~2,respectively.The dielectric loss is only 3.3%at 550℃.In addition,this ceramic exhibited excellent thermal stability,with the d₃₃value of the ceramic being 95.2% of its original value when annealed at 750℃.These properties indicate that the Co/W co-doped Na_0.5Bi_2.5Nb₂O₉-based ceramics have potential application in the high-temperature field.Finally,（Na Bi）_0.5-x（LiCe）_xBi₂Nb_1.99(Co_1/3W_2/3)_0.01O₉（NBNCW-x LC,0.00≤x≤0.12）bismuth layered piezoelectric ceramics were obtained by（Li Ce）co-doping Na_0.5Bi_2.5Nb_1.99(Co_1/3W_2/3)_0.01O₉.The effect of（LiCe）on the crystal structure and various electrical properties of NBNCW-xLC ceramics were systematically studied.Through the results of XRD,Raman,and XPS found that Ce ions in（LiCe）exist in two forms:Ce³⁺and Ce⁴⁺.（LiCe）mainly replaces the A-site ions in the perovskite-like layer,and there is also a partial Ce⁴⁺substitution of the B-site ion.The addition of（LiCe）results in the decrement of lattice distortion of NBNCW-x LC ceramic sample and the decrease of T_c,and the increase of grain size,which obviously improves the piezoelectric properties of the sample.Moreover,the reduction of impedance and increased loss may be related to the substitution of Ce⁴⁺for Nb⁵⁺of B site to produce oxygen vacancies.Among them,NBNCW-0.06LC ceramics have the best electrical properties,and its d₃₃,T_c,and P_rwere28 pC/N,761℃,and 16.3μC/cm~2,respectively.